To make a ghillie suit is to invest much time and concentration into the effort. I will show you two different ways of making a ghillie suit - one is the expensive way and the other is the poor man's way. The expensive way to make a ghillie suit would be to go out and buy a "blank".
Usually a blank will be a poncho that has twine or burlap netted into it, to allow for the stringing in the foliage. Once you have this one, what you need to do is go to the area you will be using it, either the paintball arena or the hunting grounds you are going to venture to. What you do next is to pick up the surrounding habitat, grasses and leaves.
Remember, if you use grass and leaves or other green items they will wilt very quickly. However, if you are hunting and most of what you will be in is dead leaves - that is a good thing. You assemble it by carefully weaving in different materials and making sure they stick.
Eventually after a few hours of work you might have a whole arm done - you just repeat this until the entire ghillie suit is covered. Now throw it in a pile of leaves, and kick some dirt, mud, dust, anything like that on it. Step on it too - trample it.
Once you have, you shouldn't be able to see it easily from a distance of ten feet. If you don't have the money to buy one - make one! You will need some jute or burlap netting, or any comparable netting, along with either a sewing machine, or thread and needle. You can attach the netting loosely like scales on a lizard, or you can make it tight and conform.
Personally I prefer scales, as it allows me to put more onto my ghillie suit. Once you have this assembled correctly, and your scales are on there, or whatever you have used, take it out back and make a mud puddle. Once you have a nice muddy puddle, dip the whole thing in it, and then rinse it off to get the major chunks out. Let it dry, and follow the same routine of heading out to where you will be hunting or paintballing, and get it gussied up with some twigs, grasses, leaves, and anything else.
After you have it ready, dump some mud one it, and lightly rinse it in order to make the dirt look real - well the dirt is real, but you know what I mean. Now, the difference between the two is the price, and the time it takes to assemble. Once you have it assembled and ready though, I guarantee you will love the ghillie suit you spent the most time on. The more effort and time you spend making one, the more satisfaction you will have when it is done.
Remember, after all that manufacture you need to coat it in the dirt and surrounding smells too - this will throw off the scent from animals, and also make it look more natural.
If you don't have the time or patience to make your own ghillie suit you can buy one over at http://www.ghilliesuitshop.com/